1. Field of the Invention
This present invention relates to a mobile station apparatus applied in a communication system, especially relating to the mobile station apparatus, which is able to change the access control class according to the status of low battery power for power saving.
2. Description of the Prior Art
Mobile station apparatuses, such as mobile phones, provide convenient mobile communication to users; however, mobile phones can be used to communicate only if batteries can provide enough electrical power. When electrical power is low, a conventional mobile phone sends out an alert sound or signal to remind users to change or re-charge batteries. If one user is using a mobile phone, and the electrical power is low, the user might worry that communication will be interrupted at any time; otherwise, the user need to change the battery right away, and that causes inconvenience to the user.
Conventional mobile station apparatus records a predetermined access control class for determining, under a normal condition, which base station should be used to conduct the mobile communication service. Under the normal condition, the mobile station apparatus is only allowed to camp on, for conducting the mobile communication service, through a limited predetermined number of, not all, base stations in the communication area. The mobile station apparatus is able to receive the received signal strength indicator (RSSI) issued by the base stations. Usually, the stronger the RSSI of a base station for conducting the mobile communication service, the less electrical power the mobile station apparatus consumes.
Therefore, the objective of the present invention is to provide a mobile station apparatus and method, which is able to change the access control class under the condition of low battery power, so as to allow the mobile station apparatus to conduct mobile communication service through base stations that consumes less electrical power, thus preventing the worries of users about communication interruption, or the inconvenience of changing batteries right away.